Alloying steels

ABSTRACT

A method of adding an alloying addition, such as lead, to a ferrous metal by tapping the ferrous metal from a furnace into a primary ladle and teeming the ferrous metal heated to above its customary tapping temperature from a primary ladle into a secondary ladle and at the same time adding an alloying addition to the ferrous metal during teeming and removing any toxic fumes generated by the alloying addition. The ferrous metal is held in the secondary ladle until its temperature is approximately equal to its customary teeming temperature whereupon the ferrous metal is teemed from the secondary ladle into moulds.

United States Patent Davies et al.

ALLOYING STEELS Inventors: Emrys Davies, Degan y; John Roy Rippon, Sheffield, both of England Assignee: British Steel Corportion, London,

England Filed: Mar. 15, 1973 Appl. No.: 341,731

Related US. Application Data Continuation-impart of Ser No. 80,608, Oct 14 1970, abandoned.

US. Cl 75/129, 75/46, 75/58 Int. Cl. C22c 33/00 Field of Search 75/129, 46, 58

References Cited UNITED STATES PATENTS 3/1964 Hornak 75/129 3,336,132 4/1967 McCoy 75/46 3,467,167 9/1969 Mabin 75/129 3,565,605 2/1971 Vayssiere 75/46 3,671,224 6/1972 North r 75/129 3,729,309 4/1973 Kawawa 75/129 Primary ExaminerL. Dewayne Rutledge Assistant Examiner-Peter D. Rosenberg Attorney, Agent, or FirmBacon & Thomas [5 7 ABSTRACT A method of adding an alloying addition, such as lead, to a ferrous metal by tapping the ferrous metal from a furnace into a primary ladle and teeming the ferrous metal heated to above its customary tapping temperature from a primary ladle into a secondary ladle and at the same time adding an alloying addition to the ferrous metal during teeming and removing any toxic fumes generated by the alloying addition. The ferrous metal is held in the secondary ladle until its temperature is approximately equal to its customary teeming temperature whereupon the ferrous metal is teemed from the secondary ladle into moulds.

14 Claims, 5 Drawing Figures PATENTEUUBT 1 SIM SHEET 1 [IF 4 FIG].

ALLOYING STEELS This application is a continuation-in-part of application Ser. No. 80,608, filed Oct. 14, 1970, and now abandoned.

The invention relates to the addition to iron and alloys of iron, hereinafter all referred to as ferrous metals, of an alloying addition and particularly an alloying addition for the purpose of improving the machinability of the ferrous metals,

it is well known to add a machinability improving alloying addition to ferrous'metals, but the alloying addition has in general low or negligible solid solubility in ferrous metals so that it is difficult to obtain a good recovery of the alloying addition in the ferrous metal whilst assuring that the part of the alloying addition which is retained in the ferrous metal is present in the form of uniformly distributed fine particles.

The presence of large globules of the alloying addition or of a heavy segregation thereof which are commonly found in the bottom of the ingot means that a larger part of the bottom must be discarded than the usual discard at the end of a non-alloyed rolled ingot.

Furthermore, if the alloying addition is intended to improve the machinability'of the ferrous metal, it is important that the alloying addition be dispersed as uniformly as possible throughout the ferrous metal ingot so as to improve themachinability substantially uniformly throughout the ingot as well as avoiding local segregation which would be liable to impair the mechanical properties of the ferrous metal.

Also, the fumes generated when the alloying addition is added to ferrous metals may be toxic, in which case they should be efficiently removed throughout the casting process.

The alloying addition may, for example, include one, some, or all of the elements lead, selenium and tellurium, in the form of the pure metals, or in the form of alloys, or as mineral compounds.

It is an object of the present invention to provide an improved method of adding an alloying addition to ferrous metals whereby a high recovery-of the alloying ad dition is obtained in the ingot and an ingot is produced in which the alloying addition is present in the form of a uniformly distributed and finely divided microdispersion, with a reduction in the segregation of the alloying addition as compared with most commonly used methods so that a reduced proportion of the ingot need be discarded.

A further object of the invention is the provision of an improved method as described above wherein any toxic fumes generated by the alloying addition may be efficiently and easily removed.

According to the present invention there is provided a method of adding an alloying addition to a particular ferrous metal, the method comprising the steps of heating the ferrous metal in a furnace, tapping the ferrous metal from the furnace into a primary ladle at a temperature substantially above that at which it is customarily tapped from the furnace for teeming into ingot moulds, teeming said ferrous metal from the primary ladle into the secondary ladle, adding the alloying addition during said teeming into the secondary ladle whilst removing any toxic fumes generated by the alloying addition, the teeming temperature of said ferrous metal being sufficiently high to ensure solution of said alloying addition, holding the ferrous metal in the secondary ladle until the temperature of the ferrous metal is approximately equal to the customary teeming temperature for said particular ferrous metal, and teeming the ferrous metal into moulds.

The alloying addition may be added to the stream of ferrous metal passing from the primary ladle to the secondary ladle. Alternatively, it may be added to the fcr rous metal in the secondary ladle at or adjacent to the point of entry of the stream into the metal.

Preferably, the alloying addition is not added to the ferrous metal until after the commencement of teeming so that some of the ferrous metal is already in the secondary ladle when the addition is initially made. The alloying addition is preferably added in a finely divided form.

The term ferrous metals as used herein includes alloy and other steels and the method of this invention is particularly applicable to ferrous metals of which the carbon content does not exceed 2.0 percent.

The alloying addition may be lead to improve the machinability of the ferrous metal; up to 0.50 percent lead may be added to such ferrous metals. Lead has negligible solid solubility in steel, but is slightly soluble in liquid steel, its solubility increasing as the temperature of the steel rises.

Steel is normally tapped from the furnace and cast at temperatures as near its solidification temperature as possible since the higher the casting temperature the more prone is the ingot to defects. It has been found that if lead is added to the steel during casting, or in the mould, the temperature of the steel is too low for adequate solubility of the lead and the ingot tends to contain large globules of lead and to have a heavy segregation of lead towards the bottom of the ingot.

Further, the fumes generated when lead is added to steel are highly toxic and must be efficiently removed throughout the casting process.

Similar problems are encountered with other alloying additions.

Methods hitherto used for adding a machinability improving alloying addition such as lead, for example, to plain carbon steel, have obtained recovery of 15 percent to 64 percent lead in the ingot and have required approximately 25 percent of the ingot to be discarded due to gross segregation of lead particles and normal metallurgical waste.

The use of the method of this invention for the addition of lead to a steel can result in a consistent recovery of 65 percent to percentlead although results have been achieved of over percent, and requires only the normal ingot discard to be taken to remove pipe and surface defects. Similar advantageous results are obtained with other alloying elements.

Two embodiments of the invention will now be described with reference to the accompanying drawings wherein:

FIG. 1 is a diagrammatic side elevation, partly in section, of a furnace and primary ladle for use in carrying out the method of the present invention;

FIG. 2 is a diagrammatic cross-section, to an enlarged scale, of the primary ladle of FIG. 1 and a secondary ladle for use in carrying out the method of the present invention;

FIG. 3 is a detail, to an enlarged scale, of part of the FIG. 2 illustration;

FIG. 4 is a diagrammatic cross-section, to the same scale as FIG. 2, showing the secondary ladle and an ingot mould for use in carrying out the method of the present invention; and

FIG. 5 is a view similar to that of FIG. 2, alternative form of apparatus.

Referring firstly to FIG. 1 of the drawings, there is shown a conventional electric arc furnace, indicated at 10, pivotally mounted in conventional fashion on a base 11. In FIG. 1, the furnace is shown in its tilted position for discharging its contents into a 60-tonprimary ladle 12 which is suspended, in conventional manner, from an overhead travelling crane, part of the hook of which is shown at 13. The primary ladle 12 is of conventional construction and is provided with a pouring orifice 14 which can be closed by a ceramic plug 15 controlled by a linkage 16.

Referring now toFIG. 2 of the drawings, the primary ladle can be transported by the overhead crane to a position where its discharge orifice 14 is located above a secondary ladle 17 positioned in a pit 18 in the floor of the melting shop. The secondary ladle 17 is of conventional construction and is provided with a refractory lined steel fume hood 19 which is connected by ducting 20 to a fixed ducting 21 leading to conventional fume extractor plant 22. The hood 19 is mounted on an arm 23 so that it can be pivoted about an axis 24 to enable an overhead crane to gain access to the secondary ladle l7 and lift the ladle out of the pit 18 when the contents of the primaryv ladle 12 have been discharged inthe secondary ladle 17.

The secondary ladle 17 has a discharge orifice 25 which can be closed by a refractory plug 26 controlled by a mechanical linkage 27., 1

In order to introduce an alloying addition to the stream of metal issuing from the primary ladle 12 into the secondary ladle 17 a conventional pressure gun 28 is provided which feeds the alloying addition from a pressurised hopper 29 via a nozzle 28a (FIG. 3) in the form of an open-ended funnel with a solid central cone which disperses the lead shot into a spray. FIG. 3 shows the relative disposition of the discharge orifice 14 of the primary ladle l2 and the nozzle 28a of the pressure gun 28 in more detail.

Referring now particularly to FIG. 4 of the drawings, the secondary ladle 17 can be moved by the abovementioned overhead crane to a position where its discharge orifice 25 is positioned over the ingate of a set of eight ingot moulds 28b arranged for bottom casting (uphill teeming) in conventional manner.

Movable ducting 29a is provided to cover the eight ingot moulds and the ingate. The ducting 29 extends to fixed ducting'30 which leads to a conventional fume extractor plant.

By way of example, the addition of lead to a low alloy steel using the above apparatus will now be described. In this example the following procedures were carried showing an out.

The steel of the present example was made in a 60- ton electric arc furnace 10 and was a low alloy steel having a furnace analysis as set out below Carbon 018% Manganese 0.61% Silicon 0.23% Sulphur 0.036% Phosphorus 0.024%

-Continued Nickel 1.77% Chromium 0.29% Molybdenum 0.27%

the balance being iron and the normal impurities found in a low alloy steel.

The steel was tapped from the furnace 10 by tilting it to the position shown in FIG. 1 so that the ste'elissued in a stream 32 and entered the 60-ton primary ladle 12 at a temperature of l,680C, that is at approximately 70C above its customary tapping temperature.

When the primary ladle 12 was full the furnace 10 was returned to its upright position and the ladle 12 was lifted and transported by the overhead crane until it was positioned over the secondary ladle 17 in the position shown in FIG. 2. The mechanical linkage 16 was then operated to lift the ceramic plug 15 to enable the steel within the primary ladle to issue from the discharge orifice 14 in a stream 32 and enter the secondary ladle 17, the orifice 25 of the secondary ladle 17 being closed by the ceramic plug 26. In the present example, the steel was teemed from the primary ladle 12 into the secondary ladle 17 at a temperature of approximately 1,625C,'the discharge orifice 14 was 3 inches in diameter and the total teeming time from the primary ladle was 10 minutes.

Forty seconds after the start of teeming, lead, in the form of line lead shot, was expelled from the pressure gun 28 into the stream 32a of steel passing from the primary ladle to the secondary ladle. The lead was added for-5 minutes 40 seconds and a total of 330 pounds of lead was added.

During the teeming operation the extractor plant 22 was operated to withdraw the toxic fumes generated by thelead on addition to the steel until a slag was formed on the surface of the steel in the secondary ladle, which effectively prevented the escape of further toxic fumes.

The high temperature 'of the steel ensured the solution of the lead addition, and the turbulence created in the steel in tlie secondary ladle 17 by teeming the steel from the primary to the secondary ladle, and the turbulence in the stream itself, ensured distribution of the lead.

The steel was held in the secondary ladle 17 until the temperature of the steel was approximately l,580C, i.e., the customary teeming temperature of the steel, thus avoiding the risk of ingot defects due to high pouring temperature.

Whilst the steel was cooling in the secondary ladle 17 to its customary teeming temperature the primary ladle 12 was removed by the overhead crane and the fume hood 19 was pivoted about its axis 24, the overhead crane was then engaged with the secondary ladle l7 and the ladle was lifted and transported to a further position where its discharge orifice 25 was positioned above the ingate of the ingot moulds 28b, as shown in FIG. 4.

When the steel had cooled to its customary teeming temperature the linkage 27 was operated to lift the ceramic plug 26 and so enable the steel in the secondary ladle 17 to leave the discharge orifice 25 in a stream 33 and enter the ingate of the ingot moulds 28b in conventional manner. During this operation the fume extractor plant 22 was operated to remove any further toxic fumes given off during the casting operation.

The ingots produced were tested to determine thelead distribution and content. The tests performed were as follows.

A photographic paper was soaked for 2 minutes in 5 percent sodium hydroxide solution and was placed on; a coarsely ground cross-section of a billet product of the ingot. The paper was left for 3 minutes and then placed in 5 percent sodium sulphite solution, the prints were then washed and dried.

On examination, the lead distribution shows on the paper as a brown speckled pattern, the intensity of the pattern indicating the distribution.

In a second test a short piece of the billet was sawn and placed in a small furnace at a minimum temperature of 600C. Any lead particles on the surface of the billet melt and exude, forming droplets on the billet surface. The sample was then cooled and the droplets examined. The presence of droplets gives an indication of large P rad P esen eth amrle In a third test, a short piece of sawn billet was held in a shaping machine and cuttings were taken from the whole cross-section of the billet. The lead content of the cuttings was then determined chemically in conventional manner.

In a fourth test billets obtained from the ingot were tested ultrasonically. The ultrasonic beam passed percent of the lead had been recovered in the ingot. It was also found that substantially all of the lead was uniformly distributed as a finely divided micro-dispersion and it was found to be unnecessary to discard any part of an ingot due to gross segregation of lead particles, although the normal casting discard had still to be made.

The example described is not of course to be regarded as restricting the scope of this invention since many other steel compositions can be leaded under a variety of conditions in which different conditions will obtain.

The example given relates to a low carbon, low alloy steel uphill teemed but with direct teeming (direct into open topped ingots) for the same steel lower teeming temperatures will be required, normally 20C C lower. Since the same primary/secondary ladle transfer temperature will be needed (about'l,625C) in order to ensure adequate lead solution however, then in order to reduce the cooling period following leading the secondary ladle melt can be forcibly cooled by inert gas purging before teeming. This process also assists in precluding lead precipitation.

Further examples of typical steels to which this invention has been applied are listed below, a comparison being drawn between the normal non-leaded practice and the practice according to this invention.

Quality Spec. Non-leaded Leaded U.K. U.S.A. normal normal tapping primary/ teeming or German tapping teeming temp. secondary temp. standard temp. temp. ladle transfer temp. (minimum) Low carbon En IA I620 I585 I680 I630 I590 Med.carbon En 8/9 I610 I570 I660 I620 I575 Med. carbon En l5 I6I0 I570 I660 I620 I575 156% Mn Hgh carbon En 3] I590 I550 I650 l6l0 1555 I 0 Cr Low carbon SAE 8620 I615 I575 I665 I620 1580 low NCM Med.carbon En 24 l6lO I570 I660 I620 I575 medium NCM Med.carb0n Din l7200 I610 I570 I650 I620 I575 IV4% Mn l%% Si Low carbon En 355 I620 I580 I670 I620 I580 higher NCM Med.carbon En 408 I620 I580 I670 I620 I580 3% Cr Mo Med.carbon En 418 I650 I610 I690 I650 l6l0 l%% Cr I% Al through the cross-section of the billet and a signal was Th teeming racti e adopted in this list is uphill recorded on an oscilloscope by the returning sound teeming so that both the tapping and teeming temperabeam reflected from the opposite base of the billet. Any interference with this beam by large lead particles gives an altered signal on the oscilloscope.

We have found in commercial production that it is convenient to carry out the last mentioned test on all the billets produced according to the method of the present invention as a routine quality control test whilst the first three tests described above are conducted on random samples taken from different ingot positions as is considered appropriate during a production run.

In the case of the example described above, it was found that the ingots which were produced had an average lead content of 0. I8 percent indicating that 70 tures listed are relevant to this practice. For direct teeming all the temperatures listed will be reduced by between 20C and 30C, i.e. all the temperatures except the tapping (leaded) and minimum ladle transfer temperatures which are not changed since these latter temperatures are necessary to get adequate lead solution. In all cases the tapping temperature must be such as to enable the temperature subsisting at the completion of the lead addition to be sufficient to ensure adequate lead solution.

The final teeming temperature for the leaded steels is substantially the same as that for non-leaded steels consistent with good pouring practice.

Further examples of practice pertaining to melts tapped from a larger furnace are listed below.

is approximately equal to the customary teeming temperature for said particular ferrous metal, and teeming The teeming temperatures again refer to uphill teem-- mg.

From these results it will be seen that the furnace tapping temperatures are substantially higher than is normally the case with non-leaded steels, e.g., of the order of 40C to 70C higher. The transfer temperature is customarily around l,620C but can extend up to l,655C or down to l,610C (En 3 l) but this latter figure is practically the minimum necessary to ensure adequate lead solution.

Various modifications may be made to the method described. For example instead of the lead being added to the pour stream by means of the pressure gun described above the lead may be added to the stream by any other known means e. g., by means of a gravity feed from a hopper. Moreover, instead of the lead being added to the pour stream of steel as shown in FIGS. 2 and 3, the lead may be added to the steel already in the secondary ladle 17.

Referring now to FIG. which is a view similar to F l6. 2, and in which the same reference numerals have been given to refer to corresponding parts, the lead is introduced into the steel already in the secondary ladle by means of a pressure gun which is arranged to move up as the level of the metal in the ladle rises so that the lead is introduced into the metal already in the ladle in the region adjacent the point of entry of the stream 32a into the steel already in the ladle. It has been found that the steel in the secondary ladle 17 is sufficiently turbulent in this region to ensure good dispersion of the lead.

As before instead of the lead being added to the steel already in the secondary ladle by means of the pressure gun 35 it may be introduced by any other convenient means.

Besides lead, other alloying additions may be made by the method of the present invention, for example,

selenium or tellurium, either alone or together.

In this specification all compositions are expressed in percentage by weight.

We claim:

1. A method of adding an alloying addition to a particular ferrous metal, the method comprising the steps of heating the ferrous metal in a furnace, tapping the ferrous metal from the furnace into a primary ladle at a temperature substantially above that at which itis customarily tapped from the furnace for teeming into ingot moulds, teeming the ferrous metal from the primary ladle into the secondary ladle, adding the alloying addition during said teeming into the secondary ladle whilst removing any toxic fumes generated by the alloying addition, the teeming temperature of the ferrousmetal being sufficiently high to ensure solution of said alloying addition, holding the ferrous metal in the secondary ladle until the temperature of the ferrous metal the ferrous metal into moulds.

2. A method according to claim 1, wherein the alloying addition is not added to the ferrous metal until after 4. A method according to claim 2, wherein the alloying addition is added to the ferrous metal in the secondary ladle at or adjacent to the point of entry of the stream into the metal.

5. A method according to claim 3, wherein the alloying addition is added in a finely divided form.

6. A method according to claim 5, wherein the alloying addition is lead.

7. A method according to claim 1, wherein the alloying addition is made by means of a pressure gun.

8. A method of adding an alloying addition to a particular ferrous metal, the method comprising the steps of heating the metal in a furnace, tapping the metal from the furnace into a primary ladle at a temperature substantially above that at which it is customarily tapped from the furnace for teeming into ingot moulds, teeming the metal from the primary ladle into a secondary ladle, adding the alloying addition in finely divided form to the pour stream during said teeming into the secondary ladle whilst removing any toxic fumes generated by the alloying addition, the teeming temperature of the metal being sufficiently high to-ensure solution of said alloying addition, holding the metal in the secondary ladle until the temperature thereof is approximately equal to the customary teeming temperature for said particular metal, and teeming the metal into moulds whilst removing any toxic fumes generated by the alloying addition.

9. A method according to claim 8, wherein the metal in the secondary ladle is cooled by gas purging to accelerate its rate of cooling to the customary temperature for teeming into ingot moulds.

10. A method of making leaded steel comprising the steps of making steel in a furnace, tapping the steel from the furnace into a primary ladle at a temperature of between 40C and C higher than that at which the said steel would customarily be tapped for teeming into ingot moulds, teeming the steel from the primary to a secondary ladle, adding lead to the steel during said teeming into the secondary ladle, the temperature of the steel during said teeming being not less than l,6lOC to ensure adequate lead solution, holding the leaded steel in the secondary ladle until its temperature has reached that at which un-leaded steel is customarily teemed into ingot moulds and teeming the leaded steel into such moulds.

11. A method according to claim 10, wherein any toxic fumes generated by the leaded steel are removed during teeming from the primary to the secondary ladles and during teeming from the secondary ladle into ingot'moulds.

12. A method according to claim 11, wherein the steel is teemed from the primary ladle to the secondary ladle at a temperature of between l,620C and 1,630C.

13. A method of making leaded steel according to claim 12, wherein lead is added to the stream of steel teemed from the primary to the secondary ladle, the addition being effected after the commencement of teeming.

14, A method of making leaded steel comprising the steps of making a particular steel in a furnace, tapping the steel from the furnace into a primary ladle at a temperature not more than C higher than that at which the said particular steel would customarily be tapped for teeming into ingot moulds, teeming the steel from the primary to a secondary ladle, adding lead to the steel duringsaid teeming into the secondary ladle, the temperature of the steel during such teeming being about 1,625C to ensure adequate lead solution, holding the leaded steel in the secondary ladle until its temperature has reached that at which said particular steel is cuustomarily teemed into ingot moulds, and teeming said steel into such moulds. 

1. A METHOD OF ADDING AN ALLOYING ADDITION TO A PARTICULAR FERROUS METAL, THE METHOD COMPRISING THE STEPS OF HEATING THE FERROUS METAL IN A FURNACE, TAPPING THE FERROUS METAL FROM THE FURNACE INTO A PRIMARY LADLE AT A TEMPERATURE SUBSTANTIALLY ABOVE THAT AT WHICH IT IS CUSTOMARILY TAPPED FROM THE FURNACE FRO TEEMING INTO INGOT MOULDS, TEEMING THE FERROUS METAL FROM THE PRIMARY LADLE INTO THE SECONDARY LADLE, ADDING THE ALLOYING ADDITION DURING SAID TEEMING INTO THE SECONDARY LADLE WHILST REMOVING ANY TOXIC FUMES GENERATED BY THE ALLOYING ADDITION, HOLD THE TEEMING TEMPERATURE OF THE FERROUS METAL BEING SUFFCIENTLY HIGH TO ENSURE SOLUTION OF SAID ALLOYING ADDTION, HOLDING THE FERROUS METAL IN THE SECONDARY LADLE INTIL THE TEMPERATURE OF THE FERROUS METAL IS APPROXIMATELY EQUAL TO THE CUSTOMARY TEEMING TEMPERATURE FOR SAID PARTICULAR FERROUS METAL, AND TEEMING THE FERROUS METAL INTO MOULDS.
 2. A method according to claim 1, wherein the alloying addition is not added to the ferrous metal until after the commencement of teeming so that some of the ferrous metal is already in the secondary ladle when the addition is made.
 3. A method according to claim 2, wherein the alloying addition is added to the stream of ferrous metal passing from the primary ladle to the secondary ladle.
 4. A method according to claim 2, wherein the alloying addition is added to the ferrous metal in the secondary ladle at or adjacent to the point of entry of the stream into the metal.
 5. A method according to claim 3, wherein the alloying addition is added in a finEly divided form.
 6. A method according to claim 5, wherein the alloying addition is lead.
 7. A method according to claim 1, wherein the alloying addition is made by means of a pressure gun.
 8. A method of adding an alloying addition to a particular ferrous metal, the method comprising the steps of heating the metal in a furnace, tapping the metal from the furnace into a primary ladle at a temperature substantially above that at which it is customarily tapped from the furnace for teeming into ingot moulds, teeming the metal from the primary ladle into a secondary ladle, adding the alloying addition in finely divided form to the pour stream during said teeming into the secondary ladle whilst removing any toxic fumes generated by the alloying addition, the teeming temperature of the metal being sufficiently high to ensure solution of said alloying addition, holding the metal in the secondary ladle until the temperature thereof is approximately equal to the customary teeming temperature for said particular metal, and teeming the metal into moulds whilst removing any toxic fumes generated by the alloying addition.
 9. A method according to claim 8, wherein the metal in the secondary ladle is cooled by gas purging to accelerate its rate of cooling to the customary temperature for teeming into ingot moulds.
 10. A method of making leaded steel comprising the steps of making steel in a furnace, tapping the steel from the furnace into a primary ladle at a temperature of between 40*C and 70*C higher than that at which the said steel would customarily be tapped for teeming into ingot moulds, teeming the steel from the primary to a secondary ladle, adding lead to the steel during said teeming into the secondary ladle, the temperature of the steel during said teeming being not less than 1,610*C to ensure adequate lead solution, holding the leaded steel in the secondary ladle until its temperature has reached that at which un-leaded steel is customarily teemed into ingot moulds and teeming the leaded steel into such moulds.
 11. A method according to claim 10, wherein any toxic fumes generated by the leaded steel are removed during teeming from the primary to the secondary ladles and during teeming from the secondary ladle into ingot moulds.
 12. A method according to claim 11, wherein the steel is teemed from the primary ladle to the secondary ladle at a temperature of between 1,620*C and 1,630*C.
 13. A method of making leaded steel according to claim 12, wherein lead is added to the stream of steel teemed from the primary to the secondary ladle, the addition being effected after the commencement of teeming.
 14. A method of making leaded steel comprising the steps of making a particular steel in a furnace, tapping the steel from the furnace into a primary ladle at a temperature not more than 70*C higher than that at which the said particular steel would customarily be tapped for teeming into ingot moulds, teeming the steel from the primary to a secondary ladle, adding lead to the steel during said teeming into the secondary ladle, the temperature of the steel during such teeming being about 1,625*C to ensure adequate lead solution, holding the leaded steel in the secondary ladle until its temperature has reached that at which said particular steel is cuustomarily teemed into ingot moulds, and teeming said steel into such moulds. 